The present invention concerns a crankset with no dead center position, in particular for a bicycle, including:
a fixed crankset tube,
a crankshaft rotatably mounted about a central axis within the crankset tube,
a first crank fixed to a first end of the crankshaft,
a second crank having a base rotatably mounted with respect to a second end of the crankshaft,
an eccentric member arranged in proximity to the second end of the crankshaft and connected to the tube via stopping means,
an output member mounted on the eccentric member so as to rotate about an eccentric axis which is parallel to the central axis, but offset in a direction of eccentricity, the output member being arranged to drive a mechanical transmission, and
a first and a second articulated linkage respectively connecting the crankshaft and the second crank to the output member to drive the latter.
The invention further concerns an assembly including such a crankset and an apparatus for measuring the power transmitted by the crankset.
The invention applies in particular to bicycle cranksets, but also to any other case of use of a muscle-powered crankset, for example to propel any vehicle or to power a machine, a ventilator, an electric generator, etc. Usually, the output member is provided with one or more chain wheels of a chain transmission.
In a conventional crankset, the two vertical positions of the cranks in a same radial plane constitute dead center positions, because the weight of the person pedaling cannot generate torque on the crankset in these positions. In order to overcome this drawback, it has been proposed for a long time to create a cyclical angular displacement between the cranks when they are in the top and bottom positions, as a result of bringing the chain wheels forwards in an off-center position. International Patent Application WO 97/20726 discloses such a crankset having two concentric crankshafts, whereas French Patent Nos. 763 303 and 984 583 and U.S. Pat. No. 5 067 370 disclose cranksets of this type having a single crankshaft, as in the present invention. Despite their kinematic and dynamic advantages, these cranksets have not made much impact on the market.
In the state of the art, cranksets with no dead center position and a single crankshaft have two main problems which have not been resolved in a satisfactory manner to date: sufficiently rigid and durable rotating assembly of the second crank, generally situated to the right, and a way of supporting the eccentric member which allows it to be connected to the tube in a manner which is both rigid and simple, modifying as little as possible the usual bicycle frame design.
For example, in the crankset disclosed in U.S. Pat. No. 5 067 370, the eccentric member is pivotably mounted, so that the direction of eccentricity is adjustable, on an externally threaded socket which is screwed into the crankset tube (called bottom bracket) in place of the usual socket and which thus extends the tube. The crankshaft overhangs inside this socket and beyond, to support the lever of the first articulated linkage, and further on the second crank which pivots on a nut screwed onto the crankshaft. The construction proposed in this document manifestly lacks rigidity, in particular because of the excessive overhang of the crankshaft. Such a construction requires the length and diameter of the crankshaft to be increased and cannot thus use usual components. Moreover, the mounting and dismantling of the crankset, operations which are required by current maintenance or the replacement of certain parts, appear quite complicated.
The present invention concerns a crankset capable of avoiding the aforementioned drawbacks, in particular so as to provide a high level of rigidity and to allow certain standard conventional crankset parts to be used, in particular the crankshaft and the elements which support the latter in the crankset tube.
Another particular object consists in arranging the crankset mechanism in a removable sub-assembly which can easily be mounted in place of the corresponding mechanism of a conventional crankset.
Another particular object is to allow easy adjustment of the direction of eccentricity of the crankset.
A further particular object consists in incorporating in the crankset a device for measuring the driving torque generated by the person pedaling.
According to a first aspect, the invention concerns a crankset of the type indicated in the preamble, characterized in that the second end of the crankshaft is provided with support hub on which the eccentric member and the second crank are rotatably mounted by respective bearings, the support hub being provided with a lever forming part of the first articulated linkage.
As a result, the second crank arm, the output member and the entire mechanism which assures the elimination of dead center positions are supported by the hub and can be mounted in advance on the latter in the form of a sub-assembly. Moreover, the hub can be dimensioned so as to have a desired rigidity. It may either be made integral with the crankshaft, or formed of a distinct part, for example arranged to be fitted in place of an ordinary crank on the end of a crankshaft available on the market.
A considerable advantage is that the bearings carried by the hub, especially those of the second crank, can have an inner diameter which is markedly larger than the outer diameter of the crankshaft, and can thus assure a high level of rigidity, bear non-radial loads without damage and have a long service life.
In a particularly advantageous embodiment of a crankset according to the invention, the crankset includes a device for measuring the reaction torque exerted on the eccentric member by the stopping means. This device can include a single sensor, in the form of a force sensor incorporated in the stopping means, i.e. the means preventing the rotation of the eccentric member.
According to another aspect of the present invention, there is provided an assembly including such a crankset, provided with a reaction torque measuring device, and an apparatus for measuring the energy transmitted by the crankset, said apparatus including the device for measuring the reaction torque exerted on the eccentric member by the stopping means. This device can include only one sensor, i.e. a force sensor, incorporated in the stopping means. This sensor has the great advantage of being stationary and can thus easily transmit its output signal to the measuring device mounted, for example, on the bicycle frame or handlebars. The measuring apparatus can include means for calculating and displaying a power on the basis of the measured energy.